Why does the word potable exist? Isn’t drinkable easier to learn? I’ve been thinking about this for a few minutes and did some searches, which turned up (mostly) nothing.
I started with a Google Battle of potable water vs drinkable water. That’s a lie. I started with potable vs drinkable and then later thought that perhaps drinkable may refer to liquids other than water. Regardless, it’s 2,270,000 for potable water vs 714,000 for drinkable water.
I also initially took a look at the story with Google Books NGram Viewer. It shows that potable has become more common over time, not less.
Maybe the etymology has something to show? The Online Etymology Dictionary doesn’t offer much insight; potable is derived originally from the Latin verb potare “to drink”.
Still not satisfied, I tried a few searches which eventually led me to The Word Detective, which offers a better etymology but only suggests that English grammarians favor Latin expressions. I doubt that explains the increasing trend (though I can’t fault The Word Detective for a post from 1999; rather I have to applaud anyone for keeping archives from then).
The rising trend may be the result of increasing standards for clean water and perhaps also increasing use of non-potable water (e.g., fire hydrants, irrigation). However, I still don’t have an explanation for the preference of potable over drinkable. I’m truly stumped (for now…)